pgstat: add WAL receiver status view & SRF

This new view provides insight into the state of a running WAL receiver
in a HOT standby node.
The information returned includes the PID of the WAL receiver process,
its status (stopped, starting, streaming, etc), start LSN and TLI, last
received LSN and TLI, timestamp of last message send and receipt, latest
end-of-WAL LSN and time, and the name of the slot (if any).

Access to the detailed data is only granted to superusers; others only
get the PID.

Author: Michael Paquier
Reviewer: Haribabu Kommi

1 files changed, 16 insertions, 0 deletions

diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 2052afdc8d..506a884e33 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -662,6 +662,22 @@ CREATE VIEW pg_stat_replication AS
     WHERE S.usesysid = U.oid AND
             S.pid = W.pid;
 
+CREATE VIEW pg_stat_wal_receiver AS
+    SELECT
+            s.pid,
+            s.status,
+            s.receive_start_lsn,
+            s.receive_start_tli,
+            s.received_lsn,
+            s.received_tli,
+            s.last_msg_send_time,
+            s.last_msg_receipt_time,
+            s.latest_end_lsn,
+            s.latest_end_time,
+            s.slot_name
+    FROM pg_stat_get_wal_receiver() s
+    WHERE s.pid IS NOT NULL;
+
 CREATE VIEW pg_stat_ssl AS
     SELECT
             S.pid,